An aqueous solution of ethanol (MM = 46.07 g/mol) has a molality of 12.15 m and a density of 1.100 g/mL. What is the molarity of ethanol in the solution?

Answer 1

Molarity = M = mol/L We need to find moles and liters of ethanol)

Let’s find the moles first.

Molality (m) = moles of solute / mass of solvent in kg

molality given = 12.15 m or 12.15 mol/ kg

we have to cancel out our units until we’re left with moles

12.15 mol * 1kg * 100 g = 1.215 moles of ethanol

kg 1000 g

Next let’s find the mass (g) of ethanol which will lead us to the volume (L)

1.215 mol * 46.07 g = 55.975 g

mol

Assume mass of solvent is 100 g

mass of solution = 55.975 g + 100 g = 155.975 g

Density = mass/volume = g/L

155.975 g * 1 mL * 1 L = .141795 L

1.100 g 1000 mL

Now that we have our moles and volume we can find our molarity.

Molarity = mol/ L

1.215 mol = 8.5687 M = 8.57 M

.141795 L